A simple method is proposed for the calculation of any type of P-T curve for the most general case of two-parameter equations of state in the single-phase area. For each component parameter, temperature dependency can be expressed on the basis of any analytical function; for the mixture, any mixing rule can be considered for any parameter. For the construction of these curves, the numerical algorithm is completely described. This method is illustrated for the Joule-Thomson inversion and Boyle curves.